RTC is going to be a battery issue. Replace the battery, then set the clock in the locale settings.
ACFail is power-related. you could try re-seating the power supply, reseating the plug that goes onto the backplane, reseating the motherboard, or swapping with a known-good power supply.
If you're going to try fixing the battery OR reseating the motherboard, make sure you know the process.
Turn off power supply, pull out power supply, (to make extra sure, unplug the big plug from the power box inside too)
ONLY THEN can you pull out and push in the motherboard safely into the backplane without risking frying the motherboard or video card.